Functional characterization of the D188V mutation in neuronal voltage-gated sodium channel causing generalized epilepsy with febrile seizures plus (GEFS)

Mutations in the alpha 1 subunit of the voltage-gated sodium channel (SCN1A) have been increasingly recognized as an important cause of familial epilepsy in humans. However, the functional consequences of these mutations remain largely unknown. We identified a mutation (D188V) in SCN1A segregating with generalized epilepsy with febrile seizures (GEFS) in a large kindred. Compared to wild-type sodium channels, in vitro expression of channels harboring the D188V mutation were found to be more resistant to the decline in amplitude that is normally observed over the course of high frequency pulse trains. This small change on a single aspect of channel function is compatible with an increase in membrane excitability, such as during sustained and uncontrolled neuronal discharges. These data suggest that this specific effect on sodium channel function could be a general mechanism in the pathophysiology of epilepsies caused by mutations in sodium channels in humans.